Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-04-14
2003-10-14
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S066000, C525S069000
Reexamination Certificate
active
06632879
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to crosslinkable polymer blend compositions. This invention particularly relates to such compositions wherein crosslinking occurs at least partially through a silane moiety, preferably a hydrolyzable silane moiety such as an alkoxy silane. Skilled artisans recognize that a preferred starting material to graft such a moiety onto a polymer backbone via a free radical mechanism is a vinyl silane, preferably a vinyl alkoxy silane. This invention also relates particularly to polymer compositions that include thermoplastic polyurethane, a first olefin graft polymer and, optionally, a compatibilizing polymer. The first graft polymer includes at least one silane moiety and, optionally, at least one acid or anhydride moiety. Where the first graft polymer contains both moieties, addition of a compatibilizing polymer provides no substantial improvement in composition tensile or compression set properties.
BACKGROUND OF THE INVENTION
A perceived need exists for a polymer blend composition that exhibits desirable thermoplastic polyurethane (TPU) properties such as mechanical (tensile) properties and abrasion resistance and desirable polyolefin properties such as low density, resistance to polar solvents and low moisture sensitivity. Such a composition should have an improved resistance to compression set, relative to its polyolefin component, while retaining sufficient tensile strength at break of the TPU component.
SUMMARY OF THE INVENTION
A first aspect of the invention is a polymer composition comprising a thermoplastic polyurethane and a first olefin graft polymer, the graft polymer including at least one first graft moiety and at least one second graft moiety, the first graft moiety being a silane moiety that promotes crosslinking of the grafted elastomer in the presence of moisture, the second graft moiety being an unsaturated organic compound that, prior to grafting, contains at least one ethylenic unsaturation and a polar functionality that promotes compatibilization of the olefin and the TPU.
A second aspect of the invention is a polymer composition comprising a thermoplastic polyurethane, a first olefin graft polymer, the graft polymer including at least one first graft moiety, the first graft moiety being a silane moiety that promotes crosslinking of the grafted elastomer in the presence of moisture, and a compatibilizing polymer. The compatibilizing polymer, also referred to as a modified polymer, is desirably selected from the group consisting of (a) ionomers and (b) random, block or graft olefin polymer that have, in a main or side chain thereof, an unsaturated organic compound that, prior to incorporation into the copolymer or grafting thereto, contains at least one ethylenic unsaturation and a polar functionality that promotes compatibilization of the olefin and the TPU. The unsaturated organic compound, also known as a functional group, is selected from the group consisting of carboxylic acids, carboxylate esters, carboxylic acid anhydrides, carboxylate salts, amides, epoxies, hydroxys, and acyloxys. The modified polyolefin preferably contains a grafted polar functionality (e.g. an anhydride). Skilled artisans understand that incorporation of the organic compound into a polymer backbone or grafting the organic compound onto the polymer backbone necessarily converts the ethylenic unsaturation to a saturated moiety. An alternated preferable modified polyolefin is an ethylene copolymer that has polymerized therein a polar comonomer (e.g. an acrylic or methacrylic acid functionality) and is at least partially neutralized by a reaction with an ionizable metal compound to yield an ionomer.
DESCRIPTION OF PREFERRED EMBODIMENTS
Unless otherwise stated herein, all ranges include both end points.
A “modified polyolefin” typically includes an olefin monomer such as ethylene, propylene or another alpha-olefin monomer that contains up to twenty carbon atoms as well as a vinyl functional group containing monomer. The latter monomer includes, for example, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, vinyl acetate, vinyl butyrate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, sodium acrylate, and zinc acrylate.
TPUs suitable for use in compositions of the present invention include those described in U.S. Pat. No. 4,883,837 (Zabrocki), the relevant teachings of which are incorporated herein by reference for purposes of U.S. patent practice. See, e.g., column 4, line 12 through column 6, line 5. As noted therein, any TPU may be used so long as it is thermoplastic in nature. This means that it is prepared from substantially difunctional ingredients such as an organic diisocyanate. A representative teaching on the preparation of TPU materials may be found in
Polyurethanes: Chemistry and Technology Part II
, Saunders and Frisch, 1964, pages 767-769, Interscience Publishers, New York, N.Y. and
Polyurethane Handbook
, Edited by G. Oertel, 1985, pages 405-417, Hanser Publications, distributed in the United States by Macmillan Publishing Co., Inc., New York, N.Y. Specific teachings may be found in a number of U.S. patents including, for example, U.S. Pat. Nos. 4,245,081; 4,371,684; 4,379,904; 4,447,590; 4,523,005; 4,621,113 and 4,631,329. The relevant teachings of the foregoing patents and texts are incorporated herein by reference for purposes of U.S. patent practice.
Preferred TPUs included polymers prepared from a mixture comprising an organic diisocyanate, at least one polymeric diol and at least one difunctional extender. The TPU may be prepared by the prepolymer, quasi-prepolymer, or one-shot methods in accordance with methods described in the incorporated references cited above.
Any of the organic diisocyanates previously used in TPU preparation can be used herein, including aromatic, aliphatic, and cycloaliphatic diisocyanates, and mixtures thereof.
The TPUs are present in an amount that is sufficient to impart desirable TPU properties to the compositions without being so high that it effectively eliminates cost advantages, performance benefits or both that result from inclusion of a polyolefin. The amount is desirably sufficient to provide a composition that has compression set and tensile strength values that exceed what one would expect using a monotonic (straight-line) rule of mixture approach for the TPU and polyolefin. The amount of TPU is preferably from 5 to 95 percent by weight (wt %), more preferably from 30 to 85 wt %, based on total composition weight. A TPU content of less than 5 wt % or greater than 95 wt %, while possible, does not appear to take full advantage of the presence of both polymers.
When one blends a TPU with a polyolefin, the resulting blend will have a morphology that varies between two extremes. At one extreme, a low TPU level relative to the polyolefin level yields a continuous polyolefin phase with discrete TPU domains dispersed therein. At the second extreme, a high TPU level relative to the polyolefin yields a continuous TPU phase with discrete polyolefin domains dispersed therein. At an intermediate point where the levels of TPU and polyolefin are equal or nearly so, the morphology shows co-continuous phases. When a compatibilizer or a polymer with a compatibilizing functionality is added to the blend, the disperse phase particle size changes relative to that of blends lacking the compatibilizer or compatibilizing functionality. The change in the disperse phase leads, in turn, to variations in blend mechanical properties relative to mechanical properties of blends that lack the compatibilizer or compatibilizing functionality.
The first olefin graft polymer is suitably prepared by grafting one or more functional groups onto an ethylene polymer.
“Ethylene polymers” means an ethylene/&agr;-olefin copolymer or diene-modified ethylene/&agr;-olefin copolymer. Illustrative ethylene polymers include ethylene/propylene (EP) copolymers, ethylene/octene (EO) copolymers, ethylene/butylene (EB) c
Brann Jeffery Edward
Cree Stephen Henry
DuPont Dow Elastomers L.L.C.
Mullis Jeffrey
LandOfFree
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